1. Field of the Invention
This invention relates to internal combustion engines, and in particular supplemental gaseous fuel supply and control system for such an engine using a liquid primary fuel.
2. Description of the Prior Art
The present invention is concerned wth an auxiliary or supplemental gaseous fuel supply and control system for an internal combustion engine utilizing a liquid fuel as a primary fuel source. For example, this invention finds application in connection with a diesel engine which is primarily supplied with diesel fuel during its operation, but which can be arranged to operate on both liquid and gaseous fuel while achieving substantially the same power output during its operation. Thus, this invention finds application in dual fuel supply systems for internal combustion engines wherein a supplemental gaseous fuel such as propane or natural gas (or any other fuel that can be supplied in gaseous form to an engine intake airstream) is provided to the intake air of an engine in conjunction with reduced amounts of its normal liquid fuel supply to obtain more economical operation of the engine under circumstances where the operational cost using the supplemental gaseous fuel is less than the cost of using the liquid fuel alone.
In the prior art, it is conventional to supply a gaseous fuel to the intake airstream of an internal combustion engine either alone or in combination with a liquid fuel. In typical gaseous fuel supply systems, a high pressure source of the normally gaseous fuel, which may be in liquid or highly compressed form at the supply source, is heated and vaporized in a vaporizer/pressure regulator device and then supplied to a suitable mixer valve in the intake air duct of an engine for admixture with the intake air in suitable proportions consistent with the fuel and power requirements of the engine. Examples of patents disclosing supplemental gas fuel supply systems for liquid fuel engines, such as diesel engines, include U.S. Pat. Nos. 2,781,030, 2,928,382 and 3,443,551. Furthermore, examples of mixing valves for supplying the gasoue fuel to the engine intake airstream are disclosed in U.S. Pat. Nos. 2,150,764, 2,311,315 and 3,948,224.
The problem intended to be solved by the invention is the slow response time of the typical pressure regulator valve that is located between the gaseous fuel supply source and the mixer valve at the intake duct of the engine, and also the tendency for intake air pressure signals to be inappropriate where an exhaust gas driven supercharger is provided in the intake air duct downstream of the gas fuel mixer valve. Since a typical installation involves running lengths of conduit between the gaseous fuel supply, the pressure regulator and the mixer valve, and since the pressure regulator is normally governed by a vacuum pressure signal originating at the mixer valve within the intake duct, there has been observed substantial delay in the response time of the pressure regulator, particularly in the environment of a diesel engine having an exhaust driven supercharger (turbocharger) used to pressurize the intake airstream. The delay is particularly severe when the rate of flow of the airstream suddenly decreases during a deceleration condition of the engine, resulting in oversupply of the gaseous fuel momentarily to the intake stream and the resulting waste of gaseous fuel. The problem is exacerbated by the fact that it is highly desirable to promote rapid opening of the pressure regulator valve when the rate of flow of the intake airstream is rapidly increasing and to also obtain rapid closing the regulator valve when the intake airstream flow rate rapidly decreases. However, it has been observed that it is more desirable for the rate of opening of the valve to be slower than the rate of closing of the valve, and that it is also highly desirable to fully open the pressure regulator valve when maximum engine power is demanded.